1. Field of the Invention
The invention relates to a medium detecting technology in an image forming apparatus to execute medium detection and execute print.
2. Related Background Art
Generally, a paper detecting sensor in a printer with former skew adjustment function is constructed as shown by FIG. 13A. Then, for example, when executing a print of manually supplying paper, an operator puts the paper 1 on a table 4 and sets the paper so as to make its front edge or its whichever corner of left and right touch a contact point position of a upper feed roller 2 and a lower feed roller 3, through a detection of the paper 1 executed by a table sensor 5, according to a command of a controlling section (not shown), a print operation is started.
The table sensor 5 generally is constructed by two of sensor substrate A (6) and sensor substrate B (7), on the sensor substrate A (6), a light emitting element 8 is installed; and on the sensor substrate B (7), a light receiving element 9. The table sensor 5 detects the paper 1 as a light penetrating type sensor. The table sensor 5 plurally arranged in a breadth direction in order to realize a free location function that not only can perform skew adjustment, but also can detect position of the paper 1 for printing, at which position soever the paper 1 is set on the table 4 in left direction or right direction.
When detected the paper 1 by the above-stated structure, as shown by FIG. 13B, firstly, a cam 11 coupled by a drive of a motor 10 turns, and a linked piece 12 drops the upper skew adjusting roller 13 to press and contact with the lower skew adjusting roller 14 so as to enter a skew adjustment mode.
Then, a skew adjusting motor 15 start to drive, the drive is transmitted to the lower skew adjusting roller 14 and a skew adjusting roller pulley 16 on the same shaft via a belt 17. Through the rotations of the upper skew adjusting roller 13 and the lower skew adjusting roller 14, the paper 1 is conveyed, and all of front edge of the paper 1 hits the contact points of the feed rollers 2 and 3 that are stopping. Because the feed force of the skew adjusting rollers 13 and 14 is very little, after the paper 1 hit, the skew adjusting rollers 13 and 14 only slip until they stop rotating.
Because the shaft direction of the feed rollers 2 and 3 is set to be parallel with the operation direction (toward the inner from the surface of the paper) of a carriage 18 which loads a head, through the above stated operations, the skew of the paper 1 is adjusted. Then, while the feed rollers 2 and 3 convey the paper 1, the skew adjusting rollers 13 and 14 open to move to positions making a movement load of the paper 1 lose, thus a paper conveyance mode is carried out, and the paper 1 is conveyed to a print position.
In the apparatus with the above stated structure, because a sensor substrate A (6) and a sensor substrate B (7) are mounted up and down, a problem occurs, that is, the number of parts such as connection cord (not shown) to connect them and the like increases, and cost become high. In order to solve such problem, as shown by FIG. 14, a sensor lever manner to mount sensor only on one direction side is used (for example, see patent document 1).
In the sensor lever manner, a sensor lever 20 having a turning pivot 19 is pressed by the passage of the paper 1 so that a shading section 21 turns with respect to the turning pivot 19. Thus, a light penetrating sensor 23 is opened from a shaded state that it is shaded by the shading section 21 when the paper 1 does not exist, and receives penetrating light. Thereby, it is detected that the paper 1 has passed.
Patent document 1: Japan patent publication H7-89643.
However, regarding the detection of the paper 1 performed by the sensor lever 20, it is performed not only while the conveyance of the paper 1, but also while the skew adjustment. Further, in the case to detect the paper 1 by the conventional sensor lever 20, such problem exists, that is, as shown by FIG. 15, when to adjust the skew, because the paper 1 turns as shown by an arrow on a-part in drawing, the paper 1 hit the side surface of the sensor lever 20, and a skew adjustment can not be executed.